Our ultimate goal will be to relate pre-pubertal bone mass to post-pubertal bone mass, and to develop a prediction model that may include any or all of the other variables. We propose to study whole body bone mineral, body size and composition, as well as diet and exercise patterns in elementary school children, ages 8 to 10, for a period of two years. We will recruit from every public elementary school within the city of Southfield in suburban Detroit, composed primarily of three different ethnic groups (White, Black and Middle Eastern). We will measure whole body bone mass and soft tissue composition (dual-energy x-ray absorptiometry), and height and weight at baseline, at the end of year 1, and at the end of year 2. We will also measure total body bone mineral and soft tissue composition in both parents and in all available grandparents of the subject. We will obtain dietary and exercise histories for the subject from the parent(s). Our specific aims for the study are: 1) To develop a cohort in two successive third grades in a suburban public school district, that can be followed annually for two years and followed-up at age 16. 2) To determine the annual rate of change in total body skeletal mass and to relate this to soft tissue composition and to change in height and weight. 3) To determine the relationship between the subject's baseline bone mass and that measured in their parents and grandparents. 4) To relate bone mass and changes therein to lifestyle variables. 5) To describe any observed ethnic or gender differences in average bone mass or its rate of change. Our long-term goal is to obtain follow-up diet and exercise data every year through the age of 16, and a follow-up bone mass measurement at age 16, in order to develop a prediction model of post-pubertal bone density status based on pre-pubertal bone mass and lifestyle, body size and familial data.